The present invention relates to methods of fabricating medical vascular catheters adapted to be inserted into a blood vessel from an incision through the skin of a patient for introducing other devices or fluids for diagnostic or therapeutic purposes and particularly methods for fabricating such catheter bodies with catheter sections of differing flexibility.
Catheters are tube-like medical instruments that are inserted into a body cavity, duct, tract, organ or blood vessel for a wide variety of diagnostic or therapeutic reasons, including delivery of diagnostic radiopaque materials, infusion of therapeutic drugs, performance of other interventional procedures, drainage of body cavities, organs or vessels, perfusion, and the like. Medical vascular catheters for each of these purposes can be introduced to numerous target sites within a patient""s body by guiding the catheter through an incision made in the patient""s skin and a blood vessel and then through the vascular system to the target site. Certain vascular catheters are introduced over a previously introduced guide wire or infusion wire and/or within a previously introduced guiding catheter or are advanced by blood flow in the vessel.
Medical vascular catheters generally comprise an elongated, flexible catheter tube or body with a catheter side wall enclosing a catheter lumen extending between a proximal catheter body end coupled to a relatively more rigid catheter hub to a distal catheter body end. The catheter body may be relatively straight or inherently curved or curved by insertion of a curved stiffening wire or guide wire through the catheter lumnen. The catheter body and catheter side wall are typically fabricated and dimensioned to minimize the catheter body outer diameter and side wall thickness and to maximize the catheter lumen diameter while retaining sufficient side wall flexibility and strength characteristics to enable the catheter to be used for the intended medical purpose.
Such medical catheters may be designed and used for diagnostic or therapeutic purposes in a wide range of catheter body sizes, lengths and configurations for accessing relatively large blood vessels, tracts, ducts or organs of the body or relatively small cardiac, neural or peripheral blood vessels that are frequently tortuous.
Guiding catheters are used to access a site in a patient""s body and are formed to have a high degree of directional control and to provide a guiding catheter lumen through which smaller diameter, therapeutic catheters having little or no directional control are advanced to the site. In the field of vascular intervention, guiding catheters are particularly useful to guide angioplasty and atherectomy catheters through the vasculature to a site of a blockage, such as, coronary, cerebral and renal sites. Typically guiding catheters have a specific distal section shape adapted and sized to facilitate insertion to the site of interest.
The requirements of a good guiding catheter include high torque transmission and pushability for advancement through the vasculature, high catheter lumen lubricity to facilitate insertion of catheters and other devices therethrough, low kinking characteristics, and good distal shape memory. Additionally it is desirable to provide a smooth and relatively soft distal tip leading surface to prevent damage to the vascular vessels during advancement. It is also desirable to provide a radiopaque marker near the distal tip of the catheter to enhance its visibility by fluoroscopy. A wide variety of guiding catheters have been developed that address these design requirements as set forth for example in U.S. Pat. No. 4,817,613 to Jaraczewski et al. A number of distal soft tips and radiopaque markers are also described in the above-referenced, commonly assigned, ""241 patent application and in commonly assigned U.S. Pat. Nos. 5,509,910 to Lunn and 5,545,149 to Brin et al. and in U.S. Pat. Nos. 4,283,447 to Flynn, 5,078,702 to Pomeranz, 5,234,416 to Macauley et al. and 5,221,270 to Parker.
Such guiding catheter bodies are typically formed with relatively long and stiff proximal sections or shafts and relatively short and soft distal tips, although short intermediate bonding segments or sections can be employed to assist bonding the soft distal tip to,the distal end of the proximal shaft as disclosed in the above-referenced ""910 and ""149 patents. Typically, the proximal section or shaft is formed of an inner tube, metal or polymeric filaments braided overlying the inner tube, and an outer tube over the braid, thereby providing a reinforced catheter shaft as disclosed in the above-referenced ""910, ""416, and ""149 patents. The distal soft tip is either formed separately and adhered to the distal end of the catheter shaft through a variety of techniques or is formed integrally as an extension of one of the outer or inner liners as disclosed in the above-referenced ""613 patent, for example. Butt welding techniques are disclosed in the above-referenced ""910, ""416, and ""149 patents, and lap joint techniques are disclosed in U.S. Pat. Nos. 4,531,943 to Van Tassel et al. and 4,551,292, issued to Fletcher et al. and in the above-referenced ""270 patent The exterior surface of the distal end of the catheter shaft is ground circumferentially using a xe2x80x9ccenterlessxe2x80x9d grinder to reduce the distal shaft wall thickness. The tip member is then fitted over the distal end of the catheter shaft to form a lap joint with the distal shaft and is then bonded to the distal shaft using an adhesive or other bonding technique.
Angiographic catheters of the type disclosed in U.S. Pat. No. 5,738,742 to Stevens are also formed with a wire braid reinforced proximal catheter section or shaft and a distal soft tip that is attached-thereto. In one approach characterized as prior art, a distal end portion of the proximal catheter shaft is centerless ground to a shape accommodating attachment of a separately formed soft distal tip that is then attached thereto. In a further approach presented by Stevens, a continuous reinforced tubing is first fabricated wherein an inner tube is formed over a mandrel, wire braid is applied over the inner tube outer wall during a continuous fabrication process, periodic sections of the wire braid are centerless ground away to expose the inner tube in those sections, and a continuous elastomeric coating is applied over the wire braid and exposed inner tube sections. The continuous reinforced tubing is cut to catheter body lengths including the sections without the wire braid, and the outer layer and inner layer of the section without wire braid are thermally fused together and shaped to form an integral soft distal tip. A very similar technique is disclosed in U.S. Pat. No. 4,321,226 to Markling for fabrication of catheters of unspecified types. Other angiographic catheters employ relatively stiff polymeric materials, e.g., certain nylon blends, polyamides, polyesters, etc., to provide a relatively rigid proximal catheter shaft and other softer blends of like materials in the distal end section or distal soft tip as disclosed, for example, in U.S. Pat. No. 4,563,181 to Wijayarathna et al.
Small diameter medical catheters or xe2x80x9cmicrocathetersxe2x80x9d having a catheter body outer diameter in the range of one, French (1F; 0.33 mm) to three French (3F; 1.00 mm), are typically used in tortuous vascular passageways for diagnostic and interventional neurological techniques, such as the imaging and treatment of aneurysms, tumors, arteriovenous malformations/fistulas, and the like, in the blood vessels in the brain. Such neurological catheters must be very flexible, particularly in distal sections thereof, to pass through the tortuous regions. Difficulties in endovascular positioning, however, make it desirable to impart high tensile and column strength over at least the proximal portion of the catheter. Additionally, the blood vessels of the brain are relatively fragile, so it is desirable that the catheter have a soft, non-traurmatic exterior to prevent injury. U.S. Pat. Nos. 4,464,176 to Wijayrathna and 4,739,768 to Engelson describe such catheters consisting of an inner layer and an outer layer, where the inner layer terminates proximally of the outer layer to form a relatively more flexible distal catheter section in the range of 4.0 cm in length. A large number of designs of neurological catheters for introduction over a guidewire or that are intended to be flow directed have been described in the prior art wherein the catheter body is formed of two or three or more sections of increasing flexibility distally and terminating in a distal soft tip. Such flow directed catheters are described, for example, in U.S. Pat. No. 5,336,205 to Zenzon et al. Commonly assigned U.S. Pat. No. 5,676,659 to McGurk, discloses a microcatheter body having a continuous outer layer overlying a wire braid formed over a tubular inner liner or layer to form a reinforced proximal catheter section, a more flexible intermediate section formed of the inner and outer layer without the wire braid, and terminating in a distal soft tip or distal catheter section formed only of the outer layer. It is also suggested that the pitch or characteristics of the wire braid can be varied through the proximal catheter section to increase the flexibility of the proximal catheter section distally. The formation of these catheter sections on a discrete catheter body involves use of discrete outer tubes placed over the inner jacket, heat shrink tubes placed over the outer tubes, baking the assembly in an oven, and removing the heat shrink tubes.
Finally, infusion wires have been developed that combine the functions of a guidewire with the capability of delivering an infusate while the guidewire is positioned in a blood vessel to allow introduction of other catheters or medical devices over the infusion wire. Such infusion wires are typically formed of wire reinforced proximal catheter sections that are relatively stiff to aid in pushability and torqueability and more flexible distal catheter sections that can be curved to make turns in tortuous vasculature. One such open ended infusion wire is disclosed in U.S. Pat. No. 5,178.158 to de Toledo.
As can be seen from the prior art, many common techniques, materials and constructions are employed in the fabrication of medical catheters and infusion wires of a wide range of sizes for the various medical diagnostic and therapeutic procedures. In almost all cases, medical catheter bodies need to have relatively stiff proximal catheter sections to aid in advancing the catheter distal tip to the site of interest and a relatively soft or otherwise atraumatic distal tip to avoid damage to the vasculature, tract, duct, or cavity wall it is advanced through or to. Most such catheters for vascular use now employ one or more intermediate catheter sections of intermediate flexibility or some manner of increasing flexibility of the catheter body distally so that the distal end catheter section can be advanced through a tortuous pathway. The fabrication of these catheters can be complicated and expensive. There remains a need for a fabrication technique that simplifies fabrication steps and reduces cost while retaining desirable characteristics of the catheter body.
It is therefore an object of the present invention to simplify and reduce the cost of fabrication of medical catheters of the type described above.
The present invention provides improved fabrication methods for catheters of the type having an elongated catheter body and catheter hub at the proximal catheter body end with at least one catheter lumen extending through the catheter hub and body and to a distal catheter body end thereof, and catheters formed thereby. The catheter body is formed of at least a proximal catheter section coupled at its proximal end to the catheter hub and a distal catheter section coupled at a junction with the distal end of the proximal catheter section and terminating at a distal end of the distal catheter sections. One or more intermediate catheter sections are optionally formed between the proximal and distal catheter section. The distal catheter section can comprise a relatively short distal soft tip or a separately formed distal soft tip can be attached to the distal end of the distal catheter section.
Catheters constructed in accordance with the principles of the present invention comprise a catheter body having a proximal catheter body end and a distal catheter body end and formed of a proximal section and at least one distal section that have differing flexibilities, wherein the catheter body is formed in a process comprising the steps of: (1) forming a continuous tubular inner jacket; (2) forming short initial layer segments of an initial segment thickness along the length of the inner jacket from a material of first durometer hardness, whereby each initial layer segment is separated apart by a separation distance; (3) forming a final layer of a material of second durometer hardness in a layer thickness over the tubular inner jacket along the separation distances and over and/or against the proximal and distal initial layer ends of the initial layer segments to form a continuous catheter body tubing; (4) severing the continuous catheter body tubing into catheter body lengths including a proximal catheter section formed of the material of second durometer hardness and a distal catheter section formed of the material of first hardness; and (5) completing the catheter fabrication at the proximal catheter body end and the distal catheter body end.
In step (3), the thickness of the final layer can be less than, equal to or greater than the thickness of the initial layer segments. In step (5) or in an intermediate step between steps (3) and step (4), centerless grinding can be employed to render the catheter body diameter uniform and/or to reduce the final outer diameter of the catheter body or catheter body tubing, respectively, to remove any final layer material overlying the proximal catheter section of the catheter body.
In a first variation of the method of the present invention, in a further step between steps (2) and (3), an intermediate segment layer of a material having a further durometer hardness is formed over the tubular inner jacket in an intermediate segment length and an intermediate segment thickness in proximity to each initial layer segment. The final layer forming step (3) further comprises forming the final layer over the tubular inner jacket along the separation distances and over the initial and intermediate segment layers to form the continuous catheter body tubing. The severing step (4) further comprises severing the continuous catheter body tubing into catheter body lengths including a proximal catheter section formed of the material of second hardness an intermediate catheter section formed of the material of intermediate hardness, and a distal catheter section formed of the material of first hardness over the inner jacket.
More particularly, the first material preferably is a softer durometer material than the second material (and the intermediate material, if present) whereby the resulting distal catheter section is more flexible than the proximal catheter section, although it is possible to selectively employ a first material that is harder than the second material to provide a less flexible distal section.
The first material (and the intermediate material, if present) is preferably molded over the continuous catheter body tubing in a cylinder, although it may be molded in a linear band, e.g., as a half cylinder section. The second material is preferably molded as a cylinder over the tubular inner jacket along the separation distances and over the first layer segments (and intermediate segment layers, if present) to form a continuous, cylindrical, catheter body tubing. The first and any intermediate segment layers are preferably molded or extruded to the inner jacket with tapered end edges so that they mutually engage one another (if both are present) and the second layer in a tapered edge manner.
The tubular inner jacket can be of any construction but is preferably formed in the first step of an inner tubular layer or liner composed of a lubricious material continually formed over a wire or plastic mandrel in a coating or continuous extrusion process. The use of such materials provides a very smooth lumen surface after the mandrel is removed for introducing devices and high velocity fluids through the lumen. The tubular inner jacket is preferably reinforced by any of the reinforcement processes, including use of multiple wall layers, including preferably the use of a reinforcement layer disposed over the outer surface of the tubular inner liner. Thus, the first step further preferably comprises continuously forming a reinforcement layer over the outer surface of the tubular inner liner. The reinforcement layer preferably comprises a braided reinforcement layer composed of a filament braid, preferably employing stainless steel or polymeric filaments, which is tightly braided over the outer surface of the tubular inner liner. The other layer segments and the final layer are then formed over the braided reinforcement layer. The flexibility of the catheter body is controlled by selecting the relative lengths and mechanical characteristics of each of these components.
The invention can be practiced using further tubular inner jackets. For example, the reinforcement of the tubular inner jacket, e.g., the reinforcement layer, can be either not formed or can be selectively removed in the first step (1) to expose inner liner surface lengths along the length of the inner tubular jacket are separated apart by the separation distance. Then, the initial material layer is formed over the exposed length. If a transition or intermediate catheter section is to be formed, the intermediate hardness material layer can be formed over the reinforcement adjacent to the initial material layer as described above. Alternatively, the exposed inner liner surface can be extended to an exposed length, and the initial material and the intermediate material can be formed in adjacent layer segments over that entire length. Again, however, the intermediate hardness material layer may be alternatively formed over the exposed length.
Larger diameter angiography and guide catheters formed in accordance with the present invention can have a separately formed distal soft tip segment attached to the distal catheter body end in the final fabrication step as a distal soft tip in any of the manners described above in the prior art. In such cases, a single transition from the tubular inner liner lumen to the contiguous lumen defined by the distal soft tip exists. However, the single transition can be eliminated in catheters formed in accordance with the methods of the present invention wherein the second material and the inner jacket material are suitably selected to be soft and flexible.
Employing these techniques in the different sections of the catheter body, flexibility, tensile strength, column strength, and hoop strength may be varied as desired by selectively controlling the mechanical characteristics of one or more of the formed catheter sections. Moreover, the fabrication process of forming the segment layers over prescribed segment lengths of the tubular inner jacket and then forming the continuous catheter body tubing enhances the uniformity of the characteristics of the catheter bodies cut from the continuous catheter body tubing. Costs of fabrication are also reduced.
In the exemplary embodiments, the major proximal section of the catheter body extending from its proximal end to the distal or intermediate catheter section is the least flexible, but has excellent torque transmission and hoop strength characteristics. The distal catheter section possesses the greatest flexibility with the minimum torqueability and hoop strength. The distal and any intermediate catheter section has or have greater flexibility while retaining adequate torqueability and hoop strength to permit guiding of the catheter by itself or over a guide wire and prevent kinking and collapse of the catheter lumen.
The methods of construction involve molding and extrusion techniques that result in a continuous catheter body tubing having the catheter sections formed thereon in repetitive patterns along the length thereof. Each junction of adjoining catheter sections is integrally formed and secure from fracture in use. Catheter bodies are cut from the continuous catheter body tubing, and the catheter fabrication is completed by trimming and finishing steps. The fabrication methods are therefore efficient and less costly and result in uniform product.
This summary of the invention and the objects, advantages and features thereof have been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.